Information recording medium encoded to enable track following and method of recording

ABSTRACT

System for recording/writing on a recording medium in which there are distributed, on the tracks, groups (G0) of tracks with positive continuous components and groups (G1) of tracks with negative continuous components. In reading, the values of the different signals are integrated for each track. Then, on the one hand, a first addition circuit S1 adds up the results of integration of the first tracks of each group of tracks and, secondly, a second addition circuit S2 adds up the results of integration of the last tracks of each group of tracks. A comparison circuit (CD) compares the results of additions of the two addition circuits to correct the track-following operation.

This is a Division of application Ser. No. 08/256,907 filed on Aug. 9,1994, now U.S. Pat. No. 5,640,285 which was filed as 371 Application ofPCT/FR93/01278 filed on Dec. 21, 1993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an information recording medium, a recorder, areader and a reading method. It can be applied notably to magnetic oroptical media wherein the information elements are arranged in the formof parallel tracks. It relates more particularly to a track-followingsystem.

The invention can be applied notably to computer peripheral recordingand reading systems and to all systems of a professional type.

In particular, the invention provides solutions for track following andfor the elimination of cross-talk in fixed-head reading systems.

DISCUSSION OF BACKGROUND

Present-day systems have low track density (with a pitch of over 100μm). The tracks are separated by blank signal barriers to preventreading cross-talk. This is ensured by heads that are less wide than thetracks. The checking of the position of the edge of the tape is enoughto ensure efficient following of the track and interoperational qualityof the tapes and readers for the tracks are wide.

Fixed-head systems cannot therefore hope to have high track density.

In digital information recording systems, each information element isconstituted by positive (or zero) elements and negative elements. In thedifferent tracks, the number of positive and negative elements isdifferent. This gives rise to a non-zero continuous component.

To prevent this, a channel encoder that carries out a transcoding isused: a certain number of incoming bits will be encoded in the form of ahigher number of magnetic domains, leaving sufficient freedom toeliminate the continuous component. Use will be made, for example, ofthe 8-10 code in which an 8-bit information element is encoded by meansof 10 bits. This means that the 256 information elements possible withan 8-bit code use only 256 bits out of 1024 of a 10-bit code.

If values of +1 or -1 are assigned to the magnetic domains according totheir direction, DSV designates the integral of these values on a track.Certain 10-bit recording codes therefore make it possible to limit thevariations of the DSV around the zero value.

The invention modifies this encoding of information elements so as toenable a track-following system.

SUMMARY OF THE INVENTION

The invention therefore relates to an information recording medium inwhich the information elements are recorded in tracks located side byside, in which on each track the information elements are encoded,characterized in that the encoding of the first identified tracks isdone so that these tracks have a continuous component with a first typeof value while the encoding of the second tracks of the recording mediumis done so that these second tracks have a continuous component with asecond type of value.

The invention also relates to an information recorder positioned on aninformation medium along tracks located side by side wherein, on eachtrack, the information elements are encoded, characterized in that theencoding of the first identified tracks is done so that these trackshave a continuous component with a first type of value while theencoding of the second tracks of the recording medium is done so thatthese second tracks have a continuous component with a second type ofvalue.

The invention also relates to a reader of information elements recordedin tracks located side by side on a recording medium, characterized inthat:

an integrated circuit integrates the values of the different signals foreach track;

a first addition circuit S1 adds the integration results of the firsttracks of each packet of tracks;

a second addition circuit S2 adds the integration results of the lasttracks of each packet of tracks;

a comparison circuit compares the results of the additions of the twoaddition circuits.

Finally, the invention relates to a method of recording and readinginformation elements positioned on a recording medium in tracks locatedside by side wherein, on each track, the information elements areencoded, characterized in that the encoding of the first identifiedtracks is done so that these tracks have a continuous component with afirst type of value while the encoding of the second tracks of therecording medium is done so that these second tracks have a continuouscomponent with a second type of value.

BRIEF DESCRIPTION OF THE DRAWINGS

The different objects and characteristics of the invention can appearmore clearly from the following description and from the appendedfigures, of which:

FIG. 1 shows a method for the magneto-optical reading of a magneticrecording tape;

FIG. 2 exemplifies a recording medium such as a magnetic tape recordedaccording to the invention;

FIG. 3 shows a system for reading a magnetic tape recorded according tothe invention;

FIG. 4 shows a flow chart of a system according to the invention;

FIG. 5 shows a track-following system according to the invention;

FIGS. 6a to 6e show a cross-talk correction system according to theinvention;

FIGS. 7a, 7b show a variant of the cross-talk correction systemaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention can now be described by using, for example, a 8/10 binaryencoding with non-resetting in which a binary element 1 is representedby a change in state of the recording and a binary element 0 isrepresented by an absence of the change in state of the recording.

A code such as this is designated by: 8/10+NRZI (d,k) in which:

d: represents the minimum number of 0 bits between two 1 bits (forexample d=0)

k=represents the maximum number of 0 bits between two 1 bits (forexample k=3).

According to an appropriate encoding, it is possible to eliminate thecontinuous component and have, on each track, a DSV (Digital Sum value)that is limited and has an average zero value. To this end, for an 8-bitword giving 256 possible values, during the transcoding in 10 bits, 153code-words are chosen in the 10-bit words, these 153 code-wordspossessing a zero continuous component DC=0 (number of bits at 1 equalsnumber of bits at 0) complemented by 103 code words DC=+2 paired with103 code words DC=-2. The latter differ only by the most significant bitand are used in an encoding strategy such that:

if a word DC=+2 has appeared, then the next word that arises will bechosen such that DC=-2 so as to make the DSV zero on an average. In viewof the initialization which consists in initially choosing the codewords in a table where DC=0 or +2, the direction of compensation will besuch that a code word DC=-2 compensates for a code word DC=+2.

The track-following system makes profitable use of the existence ofnon-zero continuous component code words DC=+/-2. The idea is to makethe DSV of each track increasing or decreasing in an average wayaccording to a predefined scheme for all the tracks and to thus createan absolute track reference if it is possible, during the reading, todistinguish the tracks with increasing DSV and those with decreasingDSV.

This gives rise to a modification called "deterioration" on the 8/10encoding algorithm. It is possible to speak of "modulation of the DSV"to qualify an increasing or decreasing variation of this DSV.

In this algorithm presented by FIG. 1 (for one track):

T represents the order of deterioration. So long as T=0, the algorithmof the initial 8/10 encoder is recovered.

S defines the direction of the modulation as one with a mean value thatis increasing if S>0 and decreasing if S<0.

dsv is a variable of the state of the system which indicates whetheralteration is possible in the desired direction. dsv is a binary valuethat switches over at each word.

The method used according to the invention to make an increasing DSVconsists in not compensating for a code word DC=+2 by a code word DC=-2and altering by therefore permitting two consecutive code words DC=+2.The method for a decreasing DSV consists in compensating twice for acode word DC=+2 by a code word DC=-2 and therefore permitting two codewords with consecutive DC=-2. The alteration is made effective byreversing the variable Q' which defines the choice between a code wordDC=+2 or DC=-2 (encoder 8-10).

As shown in FIG. 2, provision is made for distributing the tracks of themagnetic medium into groups (G0, G1, G2, . . . , Gn). For example,groups of five tracks are provided for.

The tracks of the even-order groups are encoded so that each one has apositive continuous component. The tracks of the odd-order groups areencoded so that each one has a negative continuous component.

The tracks of one group can therefore be differentiated from the tracksof the neighboring groups.

At reading, the system enables the detection of the groups whose lineshave positive continuous components from those whose lines have negativecontinuous components.

For the clarity of the explanation, all that will be considered will bethe tracks located on either side of the boundaries defined as being thepassage from a track with positive continuous component to a track withnegative continuous component and vice versa.

FIG. 3 shows an exemplary embodiment of a circuit for the detection ofalignment of read heads on the recorded tracks.

A digital or analog type adder computes the sum of the DSV values of thepre-boundary tracks such as the tracks 0 of the groups G0, G1, . . . .Another adder S2 takes the sum of the DSV values of the post-boundarytracks such as the tracks 4 of the groups G0, G1, . . . .

Inverters such as IN1 invert the reading of the post-boundary tracks ofthe even-order groups and the inverters such as IN2 invert the readingof the preboundary tracks of the odd-order groups.

The summator S1 gives a detection signal when it detects a positivecontinuous component on the preboundary tracks of the even-order groupsand a negative continuous component on the pre-boundary tracks of theodd-order groups. Similarly, the summator S2 gives a detection signalwhen it detects a positive continuous component on the post-boundarytracks of the even-order groups and a negative continuous component onthe post-boundary tracks of the odd-order groups.

When the two summators S1 and S2 give an identical detection signal, thereading system is appropriately secured to the tracks to be read.

When the adder S1 gives a detection signal higher than that of the adderS2, it means that the reading system is offset by at least one track inone direction (towards the left in FIG. 3).

A circuit CD detects the direction of offset and gives a track-followingcorrection signal. This track-following correction signal acts on afollowing device such as the one shown in FIGS. 4a and 4b.

The circuit of FIG. 3 provides for processing the DSV values of thepre-boundary and post-boundary tracks. However, without departing fromthe framework of the invention, it is also possible to provide for theprocessing of a greater number of tracks.

In FIG. 3, by way of an illustration, an operation in parallel has beenshown. In fact, it is possible to carry out a cyclical exploration ofthe tracks. This explains the presence of the memories D1 and D2 whichloop the output of each adder to its input. With these memories, it ispossible to add the DSV values of the different tracks progressively.

This system has a certain degree of immunity to noise. The term noisepertains chiefly to tracks that are temporarily bad which, in the mostoptimum instances, would give a sequence of random samples defining anoise with an average value of zero and a standard deviation in N whereN is the number of samples. Experience shows that this "ideal" case isvery improbable and that a poor track, if it takes part in the trackfollowing operation, tends to greatly push the previously calculated DSVin one direction or the other. A few poor tracks could make thiscomputation uncertain and highly noise infested.

To obtain immunity against this noise, all that is taken into account bythe counters are the samples declared to be "not in erasure" i.e. abovea certain threshold of amplitude, and the number of bits of theintegrator is adapted accordingly.

FIG. 1 gives a schematic view of a system for the magneto-opticalreading of a magnetic tape.

A magneto-optical reading device (TL1) as described in the French patentapplication No. 89 17313 is placed close to a magnetic support BM(magnetic tape). It receives a beam of polarized light from atransmitter TL2 and sends back to a detector TL6 a beam whose directionof polarization is a function of the state of magnetization of the tape.

A track-following system ASS is used to orient the light beamtransmitted by the magneto-optical read device TL1 so that the differentbeams for the reading of the different tracks of the tape are accuratelypointed towards the appropriate elementary detectors Dec0, Dec1. Thistrack-following system ASS is controlled by the track-following systemmentioned here above.

The track-following system ASS can be made as shown in FIG. 5.

It has a glass plate with a parallel face TL7 positioned substantiallyin parallel to the detector TL6.

It has an electromagnet TL8 and a solenoid plunger TL9 fixedly joined tothe plate TL7. The electromagnet receives electrical informationelements pertaining to track following and enables the plate to beoriented so as to appropriately deflect the beam coming from thetransducer TL1 towards the detector TL6 and assign a track-reading beamtransmitted by the transducer TL1 to each photodiode of the detectorTL6.

The system of control by electromagnet system may be replaced by apiezoelectric control system shifting either an optical element of theimaging system or the photoelement-based sensor.

Furthermore, it is not enough for the following system to be oriented sothat the track-reading beams transmitted by the device M0 are orientedtowards the detectors Dec0, Dec1, . . . . It is still necessary for eachof these different beams to be centered as far as possible on a detectoror at least positioned in a known way on a detector.

Indeed, owing to the number of tracks recorded on the magnetic medium,these tracks are very close to one another. During reading, there maytherefore exist a cross-talk, and the reading of each track could benoise-infested by the neighboring tracks.

FIGS. 6a to 6e and 7a to 7b show a system that can be used to make thetrack-following system more precise by detecting possible cross-talkamong the tracks and, for this purpose, by balancing the cross-talk ofthe different tracks with respect to one another. This system consistsof a set of operators working sequentially on signal samples Xj comingfrom n neighboring tracks.

Referring to FIG. 6a, a description shall now be given of a cross-talkcorrection system according to the invention. According to the readingsystem of FIG. 1, the read head enables simultaneous knowledge of thesamples of all the tracks (contrary to rotating head systems where theprecision of a passage from one head to the next one is insufficient).According to this simplified example, it is assumed that the samples ofinformation elements coming from adjacent tracks are processedsimultaneously.

The information elements coming from the j-1, j and j+1 order trackswill be considered to find out the cross-talk undergone by the track jowing to the tracks j-1 and j+1.

The different information elements read on the tracks of the recordingmedium are received by an amplitude control circuit 1 whose role shallbe indicated here below. The different signals xj-1, xj, xj+1 aretransmitted to a cross-talk estimation circuit 2 and to a cross-talkcorrection circuit 5.

The cross-talk estimation circuit 2 estimates the cross-talk that mayexist from the track j-1 to the track j and from the track j+1 to thetrack 1. The estimation of a cross-talk coefficient C'jg (cross-talk ofthe track j-1 on the track) is done by computing the product of thevalue of the signal xj by unity assigned the sign of the signal xj-1. Itwill be said more simply hereinafter that the signal xj is multiplied bythe signal of the signal xj-1. Similarly, the estimation of thecross-talk coefficient C'jd (cross-talk of j+1 on j) is done bymultiplying the value of the signal xj by the sign of the signal xj+1.

FIG. 6b gives an example of a cross-talk estimation circuit wherein thesignals xj-1, xj, xj+1 arrive in series. Delay circuits 20, 21 carry outa phase resetting of the signals and a circuit 22, for example of theROM memory type, computes the coefficients of cross-talk C'jg and C'jd.

Each cross-talk coefficient C'jg and C'jd thus computed is transmittedto a filter 3g, 3d or smoothing filter which enables the computing ofthe mean Cjg or Cjd in the course of time. For this purpose, eachcoefficient is combined with the previous cross-talk coefficientpreviously computed for the same track.

FIG. 6c exemplifies a smoothing filter. This filter is explained, forexample, in relation with the cross-talk coefficient C'jg. A multipliercircuit 30 multiplies the coefficient C'jg received by a weightingcoefficient k, this coefficient k being smaller than 1. The result istransmitted to an adder 31 which receives, at a second input, thecross-talk coefficient previously computed for the same track that hadbeen kept in the memory 32 and is multiplied by the coefficient 1-k(multiplier circuit 33). Thus, there is obtained, at output, across-talk coefficient Cjg which is filtered.

FIG. 6d gives the constitution, by way of an example, of the memorycircuit 32. This memory circuit has n memory circuits 32.l to 32.n. Thenumber n is the number of tracks of the recording medium. Thus, at eachprocessing of a track, the cross-talk coefficients previously computedfor the other tracks are shifted by one memory step in such a way thatthe coefficient Cjg of a track computed at a given instant enters thememory (right-hand side) and is present in the circuits 33 and 31, nmemory steps further below, when the circuit 31 receives the followingcoefficient C'jg of the same track.

The cross-talk coefficients Cjg and Cjd thus filtered are transmitted tothe cross-talk correction circuit 5. This circuit also receives thesignals xj-1, xj and xj+1 and corrects the cross-talk of the signal xjby performing the following operation:

    xj-(Cjg.xj-1+Cjd.xj+1)

FIG. 6e exemplifies an embodiment of the cross-talk correction circuit5. This circuit has two delay circuits 50, 51 that can be used torephase the signals xj-1, xj, xj+1 which, it is assumed, are received inseries. A ROM type circuit 52 receives the cross-talk coefficients Cjgand Cjd as well as the signals xj-1 and xj+1, and givesCjg.xj-1+Cjd.xj+1 in exchange. This result is transmitted to thesubtraction circuit 53 which computes the difference between this resultand the value of the signal xj. Thus the cross-talk corrected signal x'jis obtained.

The circuit of FIG. 6a thus enable the correction of cross-talk of thesignals xj.

This circuit also enables the computation of a track-following signal tocontrol the track-following device TL5 described here above. This isachieved by means of a subtraction circuit 6 that is connected to theoutputs of the filters 3g and 3d and computes the difference between thecross-talk coefficients. To prevent any sudden variation of thecross-talk coefficients from having an immediate effect on thetrack-following device, the difference Cjg-Cjd is integrated on the ntracks possessed by the recording medium. There is obtained atrack-following signal whose average on all the tracks can be taken togive a result that is insensitive to phenomena affecting a particulartrack.

The different signals (xj) allowed into the circuit of FIG. 3a have, inprinciple, a value of -1 or +1. This is not so in reality. Under theseconditions, any notable difference may distort the working of thecircuit. This is why the amplitude control circuit mentioned here aboveis used to reduce the different signals (xj) to a value that iscomparable, in terms of absolute value for all the tracks.

FIGS. 7a, 7b show a preferred alternative embodiment according to theinvention.

FIG. 7a has a cross-talk correction circuit 5 which receives the signalsxj-1, xj, xj+1.

The cross-talk estimation circuit 2 is connected to the output of thecross-talk correction circuit 5. It is associated with an integratingfilter and therefore carries out an a posteriori computation of thecross-talk coefficients. In fact, since the cross-talk computation isdone at output of the cross-talk correction circuit 5, the cross-talkestimation circuit carries out an estimation of residual cross-talk of asignal assumed to be already corrected for cross-talk. This circuit 2works in the same way as that of FIG. 6a.

The estimated residual cross-talk coefficients ejg and ejd aretransmitted to integrating filters 4g and 4d. These filters continuallyintegrate the cross-talk coefficient.

The following is the operation carried out by the integrating filters:

    Cjg.sub.t =C'jg.sub.t-1 +k'e.sub.jg

i.e. at the instant t the new estimated value of the cross-talkcoefficient is equal to the value at the instant t-1 corrected by afraction k' of the residual error e_(jg).

This is an adaptive process according to the gradient algorithm.

FIG. 7b shows an exemplary embodiment of these filters. A circuit 40caries out a weighting, by means of a coefficient k' (smaller than ₁),of the residual cross-talk coefficient (ejg). The weighted coefficientis transmitted to an input of an addition circuit 41 whose output islooped to another input by a memory circuit 42. This memory circuit 42is constituted, for example, as shown in FIG. 6d. It can seen thereforethat the residual cross-talk coefficient ejg, weighted by thecoefficient k', is added to the value of the cross-talk coefficientpreviously computed for the same track.

The circuits 4g and 4d then transmit cross-talk coefficients Cjg and Cjdto the cross-talk correction circuit 5 which is constituted in the sameway as that of FIGS. 6a and 6e and works in the same way.

The circuit of FIG. 7a therefore gives signals corrected for cross-talkx'j.

Like the circuit of FIG. 6a, that of FIG. 7a has circuits 6 and 7 which,starting from the cross-talk coefficients Cjg and Cjd, give atrack-following signal.

It may be recalled that the processing of the track signals that hasjust been descried can be done sequentially for the different tracks.

An a posteriori estimator of residual cross-talk as described (circuits1, 1') is therefore essentially the product of the current sample (Xj)by the sign of the disturbing sample (Xj+1) (synchronous detection). Itcan be seen therefore that the system can be used to correct cross-talkamong tracks.

Furthermore, with regard to the following of tracks, given the values ofprecision of mechanical positioning that can be achieved, the boundariesof the zones with DSV>0 or <0 may be as close as 100 to 200 μm withoutcreating any positioning ambiguity.

The large number of boundaries that can thus be detected makes thesystem robust in the presence of missing tracks.

It is important to note that the modification of the rules of managementof the DSV in no way causes deterioration in the capacity of thechannel.

The identification of a track according to the invention entails not theidentification of a particular original track, which would make for afragile system, but the detection of boundaries between small packets oftracks characterized by a common property.

The identification of tracks according to the invention is as simple aspossible since it analyzes only one pre-boundary track and onepost-boundary track. It is possible, by analyzing two tracks or more oneach side of each boundary, to obtain the value of deviation at theboundary in terms of number of tracks and improve the dynamicperformance of the system.

The invention therefore relates to a cross-talk correction andtrack-following system that does not cause any deterioration of thecapacity of the multiple-track signal and tolerates defects (randomlyerroneous tracks). No special marking track is needed.

In a more improved system, the reading may be done in parallel on threeblocks of 128 tracks. It has been chosen, during writing, to make theDSVs of the tracks alternately increasing and decreasing modulo 5 tracksin a block of 128 tracks and to duplicate this pattern in the other twoblocks of 128 tracks.

The track-following system which uses only one of these blocks atreading can therefore be conveyed from one block to the other withoutmodification.

A variation modulo 5 enables, as it happens, the most efficientdistribution of the increasing DSV/decreasing DSV and decreasingDSV/increasing DSV boundaries, thus minimizing the number of thesetransitions per selection line and per data line of the matrix head.

We claim:
 1. Information recording medium in which the informationelements are recorded in tracks located side by side, in which on eachtrack the information elements are encoded, characterized in that theencoding of first identified tracks is done so that said firstidentified tracks have a continuous component with a first value whilethe encoding of second tracks of the recording medium is done so thatsaid second tracks have a continuous component with a second valuedifferent from said first value wherein each one of said firstidentified tracks is in an alternating relationship with each one ofsaid second tracks to form said side by side tracks.
 2. Medium accordingto claim 1, characterized in that the encoding of the first identifiedtracks is done so that said first identified tracks have a positivecontinuous component while the encoding of the second tracks of therecording medium is done so that said second tracks have a negativecontinuous component.
 3. Medium according to claim 1, characterized inthat the first tracks are distributed in the form of packets ofconsecutive tracks.
 4. Medium according to claim 3, characterized inthat the encoding is a digital RLL encoding in which each of the digitalpositions with zero continuous components represents an informationelement and each digital position with a positive continuous componentis paired with a digital position having a negative continuous componentto represent an information element, this information element being thusrepresented, according to choice, by one of the two digital positions,the first tracks presenting digital positions with positive continuouscomponents and the second tracks presenting digital positions withnegative continuous components.
 5. Medium according to claim 1,characterized in that it comprises a magnetic tape.
 6. Medium accordingto claim 1, characterized in that it comprises a magnetic disk or anoptical recording disk.
 7. Information recorder positioned on aninformation medium along tracks located side by side wherein, on eachtrack, the information elements are encoded, characterized in that theencoding of the first identified tracks is done so that said firstidentified tracks have a continuous component with a first value whilethe encoding of the second tracks of the recording medium is done sothat said second tracks have a continuous component with a second valuedifferent from said first value wherein each one of said firstidentified tracks is in an alternating relationship with each one ofsaid second tracks to form said side by side tracks.
 8. Recorderaccording to claim 7, characterized in that the encoding of the firstidentified tracks is done so that said first identified tracks have apositive continuous component while the encoding of the second tracks ofthe recording medium is done so that said second tracks have a negativecontinuous component.
 9. Recorder according to claim 7, characterized inthat the first tracks are distributed in the form of packets ofconsecutive tracks.
 10. Recorder according to claim 9, characterized inthat the encoding is a digital RLL encoding in which each of the digitalpositions with zero continuous components represents an informationelement and each digital position with a positive continuous componentis paired with a digital position having a negative continuous componentto represent an information element, this information element being thusrepresented, according to choice, by one of the two digital positions, acircuit choosing, for the first tracks, the digital positions withpositive continuous components and, for the second tracks, the digitalpositions with negative continuous components.
 11. A method of recordingand reading information elements positioned on a recording medium intracks located side by side wherein, on each track, the informationelements are encoded, characterized in that the encoding of firstidentified tracks is done so that said first identified tracks have acontinuous component with a first value while the encoding of the secondtracks of the recording medium is done so that said second tracks have acontinuous component with a second value different from said first valuewherein each one of said first identified tracks is in an alternatingrelationship with each one of said second tracks to form said side byside tracks.
 12. Method according to claim 11, characterized in that theencoding of the first identified tracks is done so that said firstidentified tracks have a positive continuous component while theencoding of the second tracks of the recording medium is done so thatsaid second tracks have a negative continuous component.
 13. Methodaccording to claim 11, characterized in that the first tracks aredistributed in the form of packets of consecutive tracks.
 14. Methodaccording to claim 13, characterized in that the encoding is a digitalRLL encoding in which each of the digital positions with zero continuouscomponents represents an information element and each digital positionwith a positive continuous component is paired with a digital positionhaving a negative continuous component to represent an informationelement, this information element being thus represented, according tochoice, by one of the two digital positions; and in that there arechosen, for the first tracks, the digital positions with positivecontinuous components and, for the second tracks, the digital positionswith negative continuous components.